Disconnected Quark Loop Contributions to Nucleon Structure

TL;DR

This paper computes the disconnected quark loop contributions to nucleon structure using lattice QCD, focusing on scalar, axial, and tensor charges for light and strange quarks, with advanced noise reduction techniques.

Contribution

It provides the first detailed lattice QCD calculation of disconnected contributions to nucleon charges for multiple quark flavors and channels, using improved statistical methods.

Findings

Disconnected contributions are quantified for scalar, axial, and tensor channels.

Results are obtained at near-physical pion masses with controlled excited state contamination.

The study advances understanding of nucleon structure from first principles.

Abstract

We calculate the disconnected contribution to isoscalar nucleon charges for scalar, axial and tensor channels of light and strange quarks. The calculation has been done with the Clover valence quarks on the MILC $N_f=2+1+1$ HISQ lattices whose light quark masses corresponding to the pion masses of 305 MeV and 217 MeV at $a \approx 0.12$ fm and 312 MeV at $a \approx 0.09$ fm. All-mode-averaging technique is used for the evaluation two-point functions. Disconnected quark loops are estimated by using the truncated solver method with Gaussian random noise sources. Contamination from the excited states is removed by fitting the results of various source-sink separations and operator insertions to the formula including up to the first excited state, simultaneously.